We all know how an apple a day is supposed to keep the doctor away -- now it seems the same is true for tangerines.According to research, eating the fruit could protect against heart attacks, diabetes, high cholesterol and stroke as well as staving off obesity.

Nobiletin, a pigment found in tangerine peel, is ten times more potent than a similar one derived from grapefruit. Certain compounds in the peel lowered LDL cholesterol in hamsters that had been living on a high-cholesterol diet.

The compounds, known as polymethoxylated flavones (PMFs), are antioxidants that belong to a group of plant chemicals called flavonoids. Flavonoids exist in a variety of fruits and vegetables, as well as tea and red wine.

Previous research has suggested that the compounds help guard against heart disease and cancer, and two other citrus flavonoids--hesperetin from oranges and naringenin from grapefruit--have shown early promise in lowering cholesterol.

Researchers from the University of Western Ontario, in Canada, fed two groups of mice a diet high in fats and simple sugars, reports the journal Diabetes.

The first group became obese and showed signs related to metabolic syndrome – elevated cholesterol and triglycerides, high blood levels of insulin and glucose and a fatty liver – all of which increase the risk of diabetes and heart disease.

However the second group, which had Nobiletin added to its food, gained a normal amount of weight and showed no rise in cholesterol, insulin or glucose.

They were also more sensitive to insulin and their livers were found to be less fatty.

‘And in longer-term studies, Nobiletin also protected these animals from atherosclerosis, the build-up of plaque in arteries, which can lead to a heart attack or stroke.

‘This paves the way for future studies to see if this is a suitable treatment for related conditions in people.’

Dr Huff’s previous research found a flavonoid, Naringenin, in grapefruit which also protects against obesity and metabolic syndrome.

But the tangerine flavonoid is much more potent, he said.

He explained: ‘What’s really interesting to us is that Nobiletin is ten times more potent in its protective effects compared to Naringenin, and this time, we’ve also shown Nobiletin has the ability to protect against atherosclerosis.’